diff --git a/include/xo/reader/progress_xs.hpp b/include/xo/reader/progress_xs.hpp
index 6436b117..b370a1f9 100644
--- a/include/xo/reader/progress_xs.hpp
+++ b/include/xo/reader/progress_xs.hpp
@@ -49,9 +49,9 @@ namespace xo {
 
             static void start(rp<Expression> valex,
                               optype optype,
-                              exprstatestack * p_stack);
+                              parserstatemachine * p_psm);
             static void start(rp<Expression> valex,
-                              exprstatestack * p_stack);
+                              parserstatemachine * p_psm);
 
             bool admits_f64() const;
 
diff --git a/src/reader/expect_expr_xs.cpp b/src/reader/expect_expr_xs.cpp
index cd4f4cf5..eed3b006 100644
--- a/src/reader/expect_expr_xs.cpp
+++ b/src/reader/expect_expr_xs.cpp
@@ -107,7 +107,7 @@ namespace xo {
              */
             progress_xs::start
                 (Constant<double>::make(tk.f64_value()),
-                 p_psm->p_stack_);
+                 p_psm);
         }
 
         void
diff --git a/src/reader/paren_xs.cpp b/src/reader/paren_xs.cpp
index f48d9d49..5b1974cc 100644
--- a/src/reader/paren_xs.cpp
+++ b/src/reader/paren_xs.cpp
@@ -181,9 +181,7 @@ namespace xo {
             switch (this->parenxs_type_) {
             case parenexprstatetype::lparen_0: {
                 this->parenxs_type_ = parenexprstatetype::lparen_1; /* wants on_rightparen */
-                auto p_stack = p_psm->p_stack_;
-
-                progress_xs::start(expr.promote(), p_stack);
+                progress_xs::start(expr.promote(), p_psm);
 
                 return;
             }
diff --git a/src/reader/progress_xs.cpp b/src/reader/progress_xs.cpp
index 3ad4144f..ed873e35 100644
--- a/src/reader/progress_xs.cpp
+++ b/src/reader/progress_xs.cpp
@@ -55,13 +55,13 @@ namespace xo {
         }
 
         void
-        progress_xs::start(rp<Expression> valex, optype op, exprstatestack * p_stack) {
-            p_stack->push_exprstate(progress_xs::make(valex, op));
+        progress_xs::start(rp<Expression> valex, optype op, parserstatemachine * p_psm) {
+            p_psm->push_exprstate(progress_xs::make(valex, op));
         }
 
         void
-        progress_xs::start(rp<Expression> valex, exprstatestack * p_stack) {
-            p_stack->push_exprstate(progress_xs::make(valex));
+        progress_xs::start(rp<Expression> valex, parserstatemachine * p_psm) {
+            p_psm->push_exprstate(progress_xs::make(valex));
         }
 
         progress_xs::progress_xs(rp<Expression> valex, optype op)
@@ -313,8 +313,6 @@ namespace xo {
         {
             constexpr const char * c_self_name = "progress_xs::on_operator_token";
 
-            auto p_stack = p_psm->p_stack_;
-
             if (op_type_ == optype::invalid) {
                 this->op_type_ = tk2op(tk.tk_type());
 
@@ -345,7 +343,7 @@ namespace xo {
                     std::unique_ptr<exprstate> self  = p_psm->pop_exprstate();
 
                     /* 3. replace with new progress_xs: */
-                    progress_xs::start(expr, op2, p_stack);
+                    progress_xs::start(expr, op2, p_psm);
 
                     /* infix operator must be followed by non-empty expression */
                     expect_expr_xs::start(p_psm);
@@ -366,9 +364,9 @@ namespace xo {
                     std::unique_ptr<exprstate> self = p_psm->pop_exprstate();
 
                     /* 1. replace with nested incomplete infix exprs */
-                    progress_xs::start(lhs_, op_type_, p_stack);
+                    progress_xs::start(lhs_, op_type_, p_psm);
                     expect_expr_xs::start(p_psm);
-                    progress_xs::start(rhs_, op2, p_stack);
+                    progress_xs::start(rhs_, op2, p_psm);
                     expect_expr_xs::start(p_psm);
                 }